Processing tanks of large volume, typically containing anywhere from 30,000 to 100,000 gallons of liquid are required in many different fields. Such tanks are of special interest in connection with the brewing of beer, and the distilling of liquor, but are also of interest in many other fields. In the particular case of the beer and liquor industry however, such tanks must be manufactured of stainless steel, and accordingly require to be manufactured of relatively thin gauge stainless steel to keep the expense within a reasonable limitation. Clearly, such thin walled material will be unable to withstand the hydrostatic pressures imposed by such large volumes of liquid. Accordingly, it is the common practice to provide such thin walled tanks in various shapes, with reinforcing ribs around the exterior. In addition, tanks of this kind are required to be cooled so as to control the processing temperature. Cooling jackets are therefore mounted on the exterior of the tank for this purpose.
Tanks of this kind, are usually of considerable length, and must usually be cleaned and sterilized between each usage. Cleaning and sterilization are commonly carried out with liberated steam. As a result, the tanks are subjected to substantial elevated temperatures, and consequently they are liable to extend and contract to a relatively substantial extent during use. For example, a stainless steel tank fifty feet in length might extend and contract by a distance of about one half to three quarters of an inch during such a cleaning operation, and the stresses developed by such expansion and contraction must in some way be relieved in order to prevent damage to the structure.
Clearly, it would be possible to construct a tank having a cylindrical cross section which would withstand all of the hydrostatic pressures developed, and would perform in a satisfactory manner. However, the requirements of the beer and liquor industry call for processing tanks having a flat bottom, and tanks of this shape are required in many other fields. Flat bottomed tanks of this capacity will therefore require very substantial reinforcement in order to withstand the stresses imposed upon them, and many such systems of reinforcement have been proposed. However, they have generally speaking, been unsatisfactory. When filled with water, substantial stresses were developed in the side walls, tending to bend them outwardly and the roof was then liable to cave in. Reinforcing against such stresses, particularly in the roof, is difficult since the roof, when stressed will tend to cave in between the reinforcing ribs.
In almost all such systems the stresses imposed upon the reinforcement around the tank were bending stresses, and as is well known, any element can more efficiently resist axial tensile loads than loads causing bending.